#include<stdio.h>
int main()
{
	int n = 0;
	int x = 0;
	int a = 0;
	float sum = 0.0f;
	scanf("%d", &n);
	while (a != n)
	{
		scanf("%d", &x);
		if (x >= 0 && x <= 100)
		{
			sum += x;
			a++;
		}
		if (x == -1)
			break;
	}
	sum = sum / a;
	printf("%.2f", sum);
}
